This invention relates to a piezoelectric transducer drive having temperature compensation and, more particularly, to a piezoelectric transducer which drives the dither mechanism of a ring laser gyro having a temperature compensated feedback circuit for controlling the amplitude of the displacement caused by the piezoelectric transducer drive.
The essence of a ring laser gyro is that two light waves, circulating in opposite directions around the same closed path, undergo non-reciprocal phase shifts when the path is rotated. Since the path is a laser resonant cavity, the phase shifts produce optical frequency differences between the two waves. The two frequencies heterodyne at a common photodetector, giving rise to a beat frequency directly proportional to the angular rotation rate. When the angular rotation rate of a simple, unbiased ring laser is reduced to some minimum value, the frequency split between the clockwise and counterclockwise modes of oppositely directed light waves decreases so that the separate oscillations are no longer sustained. The modes of oppositely directed light degenerate and lock at the same frequency. This degeneration is caused by the backscatter radiation which is created as the light waves are reflected from the various mirrors within the closed path which forms the ring laser gyro.
In prior art arrangements, one method of eliminating mode locking at lower angular rotation rates is to introduce mechanical dithering. Such an arrangement is shown in U.S. Pat. No. 4,115,004 entitled "Counterbalanced Oscillating Ring Laser Gyro" by Thomas J. Hutchings and Virgil E. Sanders which issued Sept. 19, 1978 and is assigned to Litton Systems, Inc.
The device shown in the Hutchings et al. U.S. Pat. No. 4,115,004 may be driven by a torque motor as described therein or by a piezoelectric transducer drive. When a piezoelectric drive is utilized, the piezoelectric crystals which form the transducer tend to produce a variable displacement or deflection as a function of the voltage applied across them. This variation is first caused by differences created within each crystal during its manufacturing. A second cause is the fact that the displacement of a piezoelectric crystal is nonlinear with respect to temperature.
In prior art circuits, it is known to utilize one semiconductor material which is affected by temperature within the circuit to offset the effects of temperature on another semiconductor material used therein. See U.S. Pat. No. 2,951,208 entitled "Temperature Controlled Semiconductor Bias Circuit" by Loy E. Barton which issued Aug. 30, 1960 and is assigned to the Radio Corporation of America. The present invention carries this concept further by utilizing a feedback circuit which includes electrical elements arranged to offset the effects of temperature upon an electro-mechanical drive mechanism while controlling the voltage applied across the mechanism.